MEMS devices are micro-machined devices or systems, generally of a micron or nanometer size and incorporating integrated micro-sized sensors, actuators, signal processors, control circuitry and other like components. Thanks to their small size, lightweight, low power consumption, low price, reliable performance and other advantages, MEMS devices have found extensive use in a variety of applications.
MEMS is a new high-end technology emerging in recent years and developing rapidly. Based on advanced semiconductor fabrication technology, MEMS devices can be massively produced with well-controlled production costs and high product consistency. Typical fabrication process of MEMS devices is a micromachining process that involves film deposition, photolithography, epitaxy, oxidation, diffusion, injection, sputtering, evaporation, etching, dicing, packaging and other necessary steps for fabricating complex three-dimensional structures.
In general, an MEMS device fabrication process involves forming a trench by etching. As a width of the trench is a crucial parameter for the performance of the MEMS device, the trench width needs to be strictly controlled. Currently, the trench width is generally required to be controlled in a range from 0.2 μm to 0.5 μm. FIG. 1 schematically shows a resulting structure after the formation of a trench 16 in a conventional method for fabricating a MEMS device 10. As illustrated, the MEMS device 10 includes a substrate 11, a nickel-iron (NiFe) layer 12 overlying the substrate 11, a tantalum nitride (TaN) layer 13 overlying the NiFe layer 12, and the trench 16 in the TaN layer 13. In this structure, after the trench 16 is formed, ashing and wet cleaning processes are further involved to remove an anti-reflective coating layer 14 and photoresist 15, both disposed over the TaN layer 13.
With further reference to FIG. 1, in the conventional fabrication method of the MEMS device 10, the trench 16 is formed principally by the following steps: providing the substrate 11; successively forming the NiFe and TaN layers 12 and 13 on the substrate 11; sequentially coating the anti-reflective coating layer 14 and the photoresist 15 on the TaN layer 13, wherein the anti-reflective coating layer 14 is implemented as a bottom anti-reflective coating (BARC) layer that underlies the photoresist 15 and can reduce the reflection of exposure light for a better absorption of the exposure energy in the photoresist 15; etching the TaN layer 13 to form the trench 16; and performing the ashing and wet cleaning processes to remove the anti-reflective coating layer 14 and the photoresist 15.
However, in the course of conventional ashing processes, the TaN layer 13 tends to react with the photoresist 15 and produces a large amount of tantalum-containing polymeric substances which cover the photoresist 15 and BARE layer and impede the removal thereof This will cause a large amount of photoresist 15 and BARC residues in the trench 16, which is detrimental to the performance of the MEMS device being fabricated.
The above said residues covered by the tantalum-containing polymeric substances are difficult to be removed by conventional ashing processes which use pure oxygen (O2) under the temperature of 250° C. In addition, although conventional intensified ashing processes using a low temperature mixture of carbon tetrafluoride (CF4) and O2 are capable of removing the residues, it tends to simultaneously broaden the trench beyond the control width limit, and in a severe situation, may cause peeling of the TaN layer near the trench. Such undesired scenarios will all adversely affect the performance of the MEMS device being fabricated.
Therefore, there is an urgent need in this art for a solution to address the performance degradation of the conventional MEMS devices caused by the photoresist and BARC residues generated in the etching process for forming the trench.